The Georgia Supreme Court will hear arguments on Monday in a class action lawsuit filed by city employees over Atlanta’s 2011 pension reform. A handful of employees representing nearly 6,000 fire, police and general workers filed suit against Atlanta in late 2013, contending that the increase in their pension contributions was in violation of their contract and, therefore, unconstitutional.

Attorneys for Mayor Kasim Reed say the city acted lawfully in reforming the under-funded pension system. A Fulton Superior Court judge ruled against the employees last year.

The workers are appealing that decision to the state’s highest court. If the judges side with employees, Atlanta could be on the hook for about $36 million in restitution. According to court filings, Atlanta anticipates that losing the legal challenge would cost the city $160 million in prospective savings over the next 30 years.